In what stands, barring injury, as the only substantial battle for a spot on the 25-man roster, touted rookie and former Portland Sea Dog Jackie Bradley Jr. will be seeking to stave off veteran Grady Sizemore, once the league’s most dynamic center fielder who is trying to resurrect a career sidetracked since 2009 by an avalanche of health issues, including microfracture surgery on both knees.

Sizemore remains the underdog, but he is ahead of even his own schedule. After two productive weeks in the care of the Red Sox’s training staff, specifically sports medicine coordinator Dan Dyrek, he was feeling good enough to play against Northeastern on Thursday. It was to be his first game since Sept. 22, 2011, with the Cleveland Indians.

“I can say that I came in here feeling really good, but the fact is, being here for probably 2 1/2, almost three weeks now, the amount I’ve spent out there and to not have any setbacks and to not come in sore and to feel I can keep pushing it every day is definitely a little bit of a surprise,” Sizemore said.

“I know I’m going to have some bumps, and I’m going to have some days when I’m not feeling as good and need to slow down. But to come out here and have pushed as far as I have and gotten the response that I have, I’m more than happy. It’s more than I could’ve asked for.”

Last month, when the Red Sox signed Sizemore to an incentive-filled contract, multiple team sources told the Boston Herald that they believed he could challenge Bradley in spring training. It was a relatively inexpensive wager — $750,000 guaranteed, with as much as $6 million in incentives based on how many days the 31-year-old spends on the major league roster and the number of plate appearances he accrues.

For his part, Bradley is hoping for a repeat of last spring. A year ago, he was a touted prospect ticketed for Triple-A. Then he got hotter than the Florida sun, and with help from an injury that put designated hitter David Ortiz on the disabled list on opening day, he made the team and started in the season opener in Yankee Stadium.

The rest of the season didn’t go quite as Bradley hoped. He wound up batting only .189 over four call-ups to the majors, leaving just enough doubt regarding his readiness for full-time major league duty.

Bradley insists he is up for the competition.

“I’m being watched. I know I am,” he said. “I’ll be fine. I promise you that.”

Ross will adjust to new rule

Catcher David Ross won’t miss getting run over on plays at the plate, but he also knows the new rules legislating against collisions will mean catchers need to make adjustments in spring training. “There’s going to be an element of learning on the fly, because rules have a way of being interpreted differently by every person,” Ross said. “There’s going to be a lot of talking in spring training to umpires about what they’re looking for. It’ll definitely be a conversation starter.”

According to the new rule, a runner can’t initiate contact with a catcher, and a catcher isn’t allowed to block the plate without possession of the ball. Violation of the rule may result in an out, an ejection or even a suspension, but when it comes to defining what it means to “initiate contact,” umpires will have to use their judgment.

“As a catcher, the main thing you’re used to doing is anticipating the throw and getting your body in the best position to receive the throw and block the plate. Now, all we’ve got to focus on is catching the ball,” Ross said. “So, we’re trying to figure out how to set ourselves up best, because in the heat of the moment I know I’m not thinking about the rule change. I’m thinking about the play at the plate. Our natural instincts are going to come into play.”

A better Buchholz

Righthanded pitcher Clay Buchholz has never made it through an entire season healthy, so the Red Sox are taking steps to see if they can help. Buchholz showed what he could do during an All-Star first half last season before missing three months with shoulder and neck injuries. Manager John Farrell suggested that improved nutrition could be one path to durability.

“To me and us, as we’ve outlined to him, it’s probably a combination of nutrition and consistent routine,” Farrell said. “That’s not to say he’s lacked in those ways, but how can we improve the nutrition to the point of giving him the fuel to continue to remain durable? And if there are times when that might not be there, are there times he’s starting to wear down the body a little more rapidly than otherwise?”

Uehara motivated to keep job

Reliever Koji Uehara told the Boston Herald that he doesn’t believe the Red Sox’s closer job is his, that he still must win it in spring training.

That was music to manager John Farrell’s ears. “As we’ve come to know, he’s a standup guy and there are no excuses,” Farrell said. “It was even refreshing to hear his comments that I don’t want to be given anything, I have to go out and earn my job again.”

Uehara also admitted he is driven by doubters who don’t believe the soon-to-be-39-year-old can repeat his magical 2013. “I don’t care about what people think,” Uehara said. “Every year is a challenge. I try to make that motivation to be better.”